The primary goal of this research is to determine the protein structure of EcoRI endonuclease by X-ray crystallographic methods. This enzyme has been crystallized by the principal investigator in a form suitable for high resolution X-ray diffraction analysis. Specifically, film data collection and multiple isomorphous derivative methods will be used. Additionally, crystallization conditions will be explored for EcoRI methylase and for complexes of these proteins with their substrate DNA site. Other restriction enzymes, such as EcoRII, will also be explored. The ultimate objective of this research is to use these enzymes as model systems to study sequence specific recognition of DNA by proteins such as that which occurs during protein mediated gene regulation.